Creating an anastomosis, or the surgical formation of a passage between two normally distinct vessels, is a critical step of many surgical procedures. This is particularly true for coronary artery bypass graft (CABG) procedures in which one or more graft vessels are joined to the coronary arteries distal to the diseased portion in order to improve the blood supply to the myocardium (heart muscle). The graft vessels typically used are the saphenous vein of the leg or the radial artery of the arm. Also, the internal mammary (IMA) artery is commonly rerouted from its original position and attached to the lower anterior descending coronary artery (LAD) to restore blood flow to the left ventricle of the heart. When using harvested vessels, an anastomosis must be performed on both the proximal and distal ends of the graft vessel. For the case using the IMA, the anastomosis is made only at the distal end, or pedicle, of the IMA.
Currently the method of hand suturing the vascular anastomosis during a CABG is preferred by surgeons. The suturing method, however, is very time consuming, requiring several minutes per anastomosis even for an experienced surgeon. In some cases the blood flow in the newly joined vessels may be poor or there may be leaks, and the surgeon must remove the stitches and repeat the suturing procedure. In surgical procedures involving multiple bypass grafts, the time accumulated for doing the suturing is very substantial, putting the patient at risk and increasing the cost of the surgical procedure. Hand suturing also requires a high level of skill and is not easily mastered by many surgeons. It is especially difficult to suture if the anastomosis site is not easily accessed or viewed.
In the CABG procedure, access to the heart is obtained via a median stemotomy in which the rib cage is split longitudinally on the midline of the chest, and the left and right rib cages are spread apart. This method allows very good access to the heart but is very traumatic to the patient, and a lengthy recovery time (1-2 weeks) in the hospital is required. More recently, a cardiac procedure known as MIDCAB (Minimally Invasive Direct Coronary Artery Bypass) using a small, left thoracotomy (incision between the ribs on the left chest) directly above the heart has become more widely used to reduce the patient's pain and recovery time. In this procedure, however, the surgical access to the heart and visibility of it are significantly reduced, and hand suturing may be more difficult than when using a median sternotomy.
A number of devices for augmentation of the suturing techniques for vascular anastomosis have been developed. These devices attempt, with varying degrees of success, to reduce the difficulty in repeatedly passing a needle and thread through the blood vessel walls. Recent examples are found in U.S. Pat. No. 5,571,090 issued to Sherts on Nov. 5, 1996, U.S. Pat. No. 4,803,984 issued to Narayanan on Feb. 14, 1989, and U.S. Pat. No. 5,545,148 issued to Wurster on Aug. 13, 1996. In Sherts and Narayanan, the individual stitches must still be made one at a time and, therefore, the procedure is still time consuming. In addition, the working ends of the Wurster and Sherts devices appear to obstruct the view of the needle tip, and so precise placement of the stitch might be difficult in some situations.
Devices incorporating rings or fittings have been tried for end-to-side anastomosis. Examples are U.S. Pat. No. 4,366,819 issued to Kaster on Jan. 4, 1983 and U.S. Pat. No. 4,657,019 issued to Walsh, et al, on Apr. 14, 1987. These devices have several disadvantages and, therefore, have not become widely used by surgeons. The devices incorporate small, separate parts which must be manipulated into the blood vessels using special tools and techniques. The steps for assembly of such devices to the blood vessels may become more difficult as less surgically invasive procedures are used. In addition, the necessary manipulation of the vessels traumatize the delicate vessel walls, thus jeopardizing the ability of the vessels to heal properly. The presence of a portion of a ring or fitting in the blood stream may also inhibit the formation of a smooth, endothelial lining on the inner wall of the vessels.
Surgical staplers have been widely used by surgeons for many surgical procedures. Circular staplers and linear stapling and cutting instruments are well known in the art for the anastomosis of bowel tissue, but have not yet been made available to surgeons in miniature versions suitable for vascular anastomosis. Circular staplers are used primarily for end-to-end anastomosis of bowel tissue. For coronary procedures, the end-to-end type of anastomosis is not preferred because it requires the coronary artery to be completely severed from its original blood supply to be joined to the graft vessel. This could only be used in relatively infrequent cases when the coronary artery is completely occluded proximal to the location for the anastomosis. Circular staplers also have been used for the end-to-side type of anastomosis on large organs such as bowel. A key disadvantage of a circular stapler for this application is that one hollow organ must be joined to the side of the other hollow organ at about a 90 degree angle. In vascular anastomosis, it is often desirable to join the graft vessel to the target vessel at an acute angle to facilitate laminar blood flow through the joined vessels, or to avoid kinking of the graft vessel. Also, the size of the passageway between the joined vessels is limited by the diameter of the graft vessel. For a side-to-side anastomosis, the passageway size can be made to very large relative to the vessel diameters by choosing the appropriate length of staple joining lines.
In the PCT application WO 97/16122 filed by Rygaard on Oct. 31, 1995, an instrument and method is shown for using a miniature, circular stapler in an end-to-side anastomosis of blood vessels. However, this device still requires substantial manipulation of the vessels as the device is assembled together and operated. This is often difficult to do with very limited access to the surgical site, and also could lead to the inability of the vessels to heal together properly. In addition, visualization of the vessels at the anastomosis while using this device is significantly obstructed by the distal end of the device.
Linear stapling and cutting instruments, usually referred to as linear cutters (see, for example, U.S. Pat. No. 5,465,895, issued to Knodel, et al, on Nov. 14, 1995 and which is hereby incorporated herein by reference) are primarily used to hemostatically transect tissues to be removed from the body, but may also be used to anastomose organs side-to-side. Such devices have proven to be time-saving, reliable, and relatively easy to use by surgeons. The current stapling devices, however, are not designed to be made into miniaturized versions that would allow them to be useful for vascular anastomosis, and, as is discussed below, there are difficulties in making miniaturized versions.
A linear cutter has two forks forming an implement on the distal end of the instrument. One fork is a metal channel adapted to receive a staple cartridge. The cartridge contains numerous surgical staples aligned longitudinally into a number (usually four or six) of rows. The other fork is a metallic anvil containing an equal number of pockets, one for each staple. When tissue is clamped between the two forks, a drive member actuated on the handle, pushes a number of wedges (usually 2) in the distal direction. The wedges bear against cam surfaces on a number of drivers within the staple cartridge, causing the drivers to push the staples out of the cartridge, through the tissue, and into the staple pockets on the anvil. As each staple is completely emitted from the cartridge, the staple forms in the anvil staple pocket, thus clinching the tissue held therebetween. As a drive member pushes the wedge in the distal direction, it also pushes a knife which is slightly proximal to the wedge. The knife cuts through all the tissue held in the forks except for at the distal most end where it stops at a location just proximal to the end of the staple lines. Then the wedges and knife are returned to their starting location either manually or by a spring return mechanism within the handle of the instrument.
When using a conventional linear cutter for creating a side-to-side anastomosis of large organs, the severed end of a first hollow organ (such as a portion of the small intestine) is placed over the anvil. Next the severed end of a second hollow organ (such as another portion of the small intestine) is placed over the staple cartridge channel. The tissue is clamped together, stapled and cut. This must then be followed by a second application of the device perpendicular to the first application in order to close the open ends of the two joined organs. The result is a passage between the two joined organs. In time, the tissues grow together, given an adequate blood supply. As the joined organs heal together, the passage between the organs straightens. More detailed descriptions along with illustrations showing the use of linear cutting staplers for side-to-side anastomosis of bowel, as well as other procedures, can be found in the Atlas of Abdominal Surgery, Braasch, et al, Chapter 10, published by W. B. Saunders Co., 1991.
Prior art linear cutters, however, are not practical for use on small blood vessels. In addition to the problems of attempting to manufacture components based on designs simply scaled down from the prior art linear cutters, there would be other difficulties with using prior art linear cutters for small vessel anastomosis. When a conventional linear cutter is used on tissue, the knife cuts through all the tissue clamped between the forks up to a location just proximal to the distal end of the staple line, severing the joined organs at their open ends where the forks are inserted. Therefore, instead of creating a closed loop passageway between the sides of the organs, an open, V-shaped passageway is created. This could cause a number of difficulties and problems when creating anastomosis in very delicate vessels such as the coronary artery.
Regardless of the above, linear cutters are simple, effective and easy to use surgical devices. Therefore there has been a desire for a linear cutter which can provide anastomosis of very small hollow organs such as blood vessels, but which overcomes the above mentioned problems. Such a device should allow the creation of a passage between the vessels in one step, after preparation of the vessels, and that the passage have an unbroken, flexible circumference. It is further desirable that the device require minimal manipulation of the blood vessels. It is also desirable to provide a device which creates the anastomosis without exposing blood flow to a significant amount of foreign material and allows rapid healing of the endothelial lining inside the blood vessels. Further, it is desirable to have such a device which is adapted to be used in traditional open cardiac procedures (CABG), minimally invasive procedures such as MIDCAB, and also adaptable to endoscopic procedures. The present invention provides such a device.